Tracking and distribution systems employ various arrangements of conveyor belts and associated components to move items along a predefined route in order to transport items to desired end locations. Item tracking systems in commercial settings may use barcode labels to identify, track, and direct these items throughout the system. Barcode labels, however, require an unobstructed and direct line of sight between the barcode reader and barcode label. The orientation, shape, and size of packages bearing barcode labels can complicate the ability of the barcode reader to read the barcode label. In contrast, radio frequency identification (“RFID”) tags do not require an unobstructed and direct line of sight between an antenna that transmits and receives radio frequency (“RF”) signals and the RFID tag, and it is known to employ RF readers in conveyor tracking systems to identify and track items moved by the conveyor bearing RFID tags.
Generally, in such an RFID system, a number of RF antennas are situated alongside, above, and/or below the conveyor belt to read RFID tags located on the various sides of packages as the packages travel along the conveyor path. A photodetector or other sensing device detects the front of a package, which triggers the system to initiate and store a package record in the system memory. The sensor's position in the conveyor path is known, and the tracking system uses this information, in combination with output data from a tachometer that corresponds to the conveyor's movement, to track the location of each package as it travels along the conveyor path between the sensor and a predefined point downstream from the sensor.
For each antenna in the system, an RF engine (separate engines may be used for the antennas, or the antennas may share a common engine) supplies a drive signal to the antenna, which radiates an electromagnetic field in response to the signal. The antenna transmits interrogation signals capable of activating RFID tags affixed to packages that pass through the electromagnetic field and receives backscattered data signals from activated tags located within or passing through the radiated field. Depending on the rate at which the antenna system sends and receives signals to and from the RFID tag, the RF tracking system may receive a signal from a given RFID tag multiple times before the tag exits the electromagnetic fields radiated by the system's antennas. The tracking system may define a predetermined area along the conveyor within the area covered by the electromagnetic field radiated by the antenna, where, if the system receives a signal from an RFID tag when a package is within the predetermined area, the system assigns the tag data from the signal to the package record corresponding to that package.
There can be uncertainty, however, in determining the correct package to which an RFID tag corresponds relying solely on the package's position in the area at the time signals are received from the tag. Since the radiated field lacks specific, defined boundaries, it can be possible that a given response may have been received from an RFID tag affixed to any of multiple packages within the predetermined area or to a package located outside the predetermined area. Thus, it may be difficult to assign specific RFID tag data to a particular package when two or more packages are simultaneously located within, or in close proximity to, the predetermined area at the time the signal was received. Systems may assign an RFID tag to a given package when the system reads the tag more times when that package is within the predetermined area than when packages upstream are in the predetermined area.